We’ve all accidentally deleted an important file — or forgotten to save a file after typing up a whole page worth of changes. The latter problem is fixed with Autosave in most modern Mac apps, and the former is usually fixable if you have a Time Machine backup setup or if the deleted file was in Dropbox (where you can undelete files or roll back changes to them for up to 30 days for free, from their site).

But what if you manage to delete a file that wasn’t backed up? Or — even worse — what if you wipe your whole backup disk without meaning to? You’re going to need a disk recovery tool, one that can undelete files. I just had this happen to my personal backup disk, and after recovering from my initial panic, took Disk Drill for a spin to see how much it could get back. This time, I wasn’t just testing an app for a review: I honestly needed the app to work.

The good news: it worked, most of the way. Here’s the good, the bad, and the ugly of disk recovery, and how to get the most of your data back if you ever find yourself in a similar situation.